1. Field of the Invention
The present invention pertains to stackable riser sections and riser covers for access risers. More particularly, the present invention pertains to connecting a series of riser sections in a way that provides improved vertical support that minimizes the effect of frost heaving and other forces due to vertical ground movement, and resists rotational forces resulting from lateral ground movement and to a removable riser cover for stackable riser sections. It further relates to the configuration of a riser cover that provides a fluid and gas tight seal to a riser section, and to structure to facilitate its removal from a riser section as well as facilitating locating the cover under ground and to the stacking of a plurality of riser covers for compact and stable shipment or storage. It also relates to a system and method of maintaining the position and shape of a riser section while the riser section is being anchored in concrete by using the riser cover for positioning and support during the anchoring process.
2. Discussion
Meters, splices, junction boxes, and other components of buried utility systems are often located inside hand-holes or manholes to enable easy access by utility workers from above ground. Often, utility systems provide such access facilities at key points, such as a major  bend in an underground cable/conduit run or location of water or gas meters and other equipment requiring servicing or inspection. Such access facilities have been constructed using pre-formed or poured concrete side retaining walls. Concrete can be expensive, particularly where the application requires a non-standard size or length, in which case setting forms and pouring concrete adds time and expense. Also, over time, the concrete can crack due to forces caused, for example, by freezing and thawing or by heavy vehicles being driven over the top of the manhole. Tiled sidewalls and concrete block are examples of other labor intensive alternatives.
Injection molded, plastic, stackable riser sections made of high density polyethylene and other rigid, light weight polymeric material are known in the art and provide a less expensive, standardized alternative that lends itself to rapid on-site customization. Riser sections can be manufactured in various heights and diameters, and a series of identically sized riser sections can be stacked to achieve a desired depth.
Depending on the soil characteristics and overhead traffic, the vertical, horizontal, and rotational forces placed upon these riser sections can be considerable. A major shortcoming of plastic riser sections lies in their tendency to deform or break when subjected to such forces. The use of vertical and horizontal strengthening ribs to alleviate this tendency is common. When placed along the exterior of the sidewall, however, these reinforcing ribs themselves often are subjected to the same vertical and horizontal forces they are intended to protect against.
U.S. Pat. No. 5,852,901 for a “Stackable Riser for On-Site Waste and Drainage Systems,” issued to Meyers, illustrates one prior art design of a plastic riser section for forming a depth-adjustable, grade-level access for underground components. The Meyers riser sections form a rigid structure intended to support heavy loads applied to the grade level access lid. Identical riser sections reinforced along portions of both the inner and outer walls are  stacked one on top of the other utilizing a single tongue and groove connection. A horizontal rib extending outward along the circumference of the external surface of the side wall of each cylindrical riser section and a plurality of vertical ribs, also on the external surface of the riser, individually anchor each riser section in the ground. A plurality of riser sections can be stacked to form a vertical, air-tight, liquid-tight, and gas-tight riser stack and cover system.
The shifting of the ground surrounding the riser stack disclosed in the Meyers patent can twist and move the stacked riser sections, knocking them out of alignment. Eventually, the shifting can lead to rupture of the stacked riser sections' sidewall. The presence of external horizontal and vertical reinforcing ribs extending along the wall of each riser, while strengthening the riser section sidewalls, also exacerbates this problem because shifting soil applies force against each exposed rib. The configuration of the tongue and groove arrangement of the riser sections disclosed in the Meyers patent also precludes the placement of supporting ribs along the full vertical length of the interior riser section wall, which lessens the sidewall's resistance to forces exerted by the shifting of the soil abutting the sidewalls and external ribs.
It is also common for one section of a riser stack to be anchored in concrete. The anchored section, generally the section defining the opening into the chamber defined by the concrete walls of an underground component, is then used as a base for the riser. Other sections are stacked on top of the anchored section to the desired height of the riser. This process involves positioning and securing a hollow riser section inside a concrete mold or form of a shape for forming the top wall of a chamber or underground component. The concrete is then poured into the mold around the riser section. The riser section can be subjected to stress during this process and may deform or break under these conditions. In addition, because it can be  made of light weight plastic, it can be difficult to keep the riser section in place while pouring the concrete because the riser section may tend to float in the concrete.
One method of preventing deformities in the riser section during anchoring involves the addition of cross braces to the inside of the riser. The braces can conform to the shape of the riser section or can simply be metal or wood rods sufficiently long to provide lateral support for opposed riser section sidewalls. This solution is imperfect, however, because the sidewall support thus provided is not uniform and may still permit deformities to occur. Additionally, this solution adds to the cost and time needed to anchor a riser section in concrete.
A variety of methods have been employed to keep a riser section in place during the anchoring process, with almost all involving construction on an ad-hoc basis in the field. One method is to place one or more elastic straps or rubber cords across the top of the concrete form, ensuring contact with the riser section in order to hold it down. This does not address side-to-side movement. One way to attempt to control this is by placing a weight or heavy object, such as a concrete block, on top of the riser section and under the elastic strap. The weight, however, may create an additional problem because it adds to the stresses being applied to the riser section sidewalls during placement of the concrete.
Another difficulty with the use of plastic riser sections is locating the riser stack after installation. Many riser access facilities are located in areas where it is easy to locate the opening, such as in streets, sidewalks, and other paved areas, or where the opening is above grade. However, access facilities frequently are located below grade level and are covered by soil and grass or other vegetation. In these situations, it may be difficult to locate the opening of the access facility when required. While a metal cover may be located using a metal detector, plastic stackable riser sections may not. One method of making plastic riser stacks locatable is to  mold one or more metal rods into the concrete wall into which a plastic riser section has been anchored. Because the concrete wall is typically lower in the ground than the riser cover, a significant amount of metal is required in order to ensure it can be detected at the surface using a conventional metal detector. This method may also create an added step in casting the wall of the box into which the bottom riser section is anchored.